They say doing structured activities with others has been shown to improve sufferersâ€™ memory and quality of life â€˜consistentlyâ€™.
The claim follows analysis of 15 studies of elderly people with mild to moderate dementia or Alzheimerâ€™s disease.
About half of the 700 participants received cognitive stimulation treatment (CST), which involved them in activities several times a week in groups of four or five.
These patients scored higher in memory tests than those visited by home helps or given medication or physical therapy, with the benefits lasting for up to three months after treatment had been completed.
The recipients of CST and their carers also noted improvements in their communication skills and general wellbeing.
Professor Bob Woods of Bangor University, who carried out the review, said the findings were â€˜the most consistent yetâ€™ in favour of psychological treatments for dementia.
He stressed that CST differs from simple â€˜brain trainingâ€™, such as doing puzzles: â€˜This is not doing the same exercises over and over again by themselves.â€™
â€˜There might be a session out of 14 which is devoted to word games and puzzles, and other sessions for reminiscing or doing something practical like baking a cake or gardening.â€™
He said further work would focus on whether CST could be carried out by family members, rather than carers, on a one-to-one basis.